The compound tetracycline, exhibits the following general structure

The numbering system of the ring nucleus is as follows:

Tetracycline as well as the 5-OH (Terramycin) and 7-Cl (Aureomycin) derivatives exist in nature, and are well known antibiotics. Natural tetracycline may be modified without losing their antibiotic properties, although certain elements of the structure must be retained. The modifications that may and may not be made to the basic tetracycline structure have been reviewed by Mitscher in The Chemistry of Tetracyclines, Chapter 6, Marcel Dekker, Publishers, New York (1978). According to Mitscher, the substituents at positions 5–9 of the tetracycline ring system may be modified without the complete loss of antibiotic properties. Changes to the basic ring system or replacement of the substituents at positions 1–4 and 10–12, however, generally lead to synthetic tetracyclines with substantially less or effectively no antimicrobial activity. Some examples of chemically modified non-antimicrobial tetracyclines (hereinafter CMT) are 4-dedimethylaminotetraccyline, 4-dedimethylaminosancycline (6-demethyl-6-deoxy-4-dedimethylaminotetracycline), 4-dedimethylaminominocycline (7-dimethylamino-4-dedimethylaminotetracycline), and 4-dedimethylaminodoxycycline (5-hydroxy-6-deoxy-4-dedimethyaminotetracycline).
Some 4-dedimethylaminotetracycline derivatives are disclosed in U.S. Pat. Nos. 3,029,284 and 5,122,519. They include 6-demethyl-6-deoxy-4-dedimethylaminotetraccyline and 5-hydroxy-6-deoxy-4-dedimethylaminotetracycline with hydrogen and other substituents at C7, and the C9 positions on the D ring. These substitutents include amino, nitro, di (lower alkyl) amino, and mono (lower alkyl) amino or halogen. The 6-demethyl-6-deoxy-4-dedimethylaminotetracycline derivatives and 5-hydroxy-6-deoxy-4-dedimethylaminotetracycline derivatives are said to be useful as antimicrobial agents.
Other 4-dedimethylaminotetracycline derivatives with an oxime group at the C4 position on the A ring are disclosed in U.S. Pat. Nos. 3,622,627 and 3,824,285. These oxime derivatives have hydrogen and halogen as substitutents at the C7 position and include 7-halo-6-demethyl-6-deoxy-4-dedimethylamino-4-oximinotetracycline, and 7-halo-5-hydroxy-6-deoxy-4-dedimethylamino-4-oximinotetracycline.
Alkylamino (NH-alkyl), and alkylhydrazone (N—NH-alkyl) groups have been substituted on the A ring at the C4 position of 4-dedimethylaminotetracycline. These compounds are known for their antimicrobial properties. See U.S. Pat. Nos. 3,345,370, 3,609,188, 3,622,627, 3,502,660, 3,509,184, 3,502,696, 3,515,731, 3,265,732, 5,122,519, 3,849,493, 3,772,363, and 3,829,453.
In addition to their antimicrobial properties, tetracyclines have been described as having a number of other uses. For example, tetracyclines are also known to inhibit the activity of collagen destructive enzymes, such as matrix metalloproteinases (MMP), including collagenases (MMP-1), gelatinase (MMP-2) and stromelysin (MMP-3). Golub et al., J. Periodont. Res. 20:12–23 (1985); Golub et al. Crit. Revs. Oral Biol. Med. 2:297–322 (1991); U.S. Pat. Nos. 4,666,897; 4,704,383; 4,935,411; 4,935,412. Also, tetracyclines have been known to inhibit wasting and protein degradation in mammalian skeletal muscle, U.S. Pat. No. 5,045,538, and to enhance IL-10 production in mammalian cells.
Furthermore, tetracyclines were reported to enhance bone protein synthesis in U.S. Pat. No. Re. 34,656, and to reduce bone resorption in organ culture in U.S. Pat. No. 4,704,383.
Similarly, U.S. Pat. No. 5,532,227 to Golub et al, discloses that tetracyclines can ameliorate the excessive glycosylation of proteins. In particular, tetracyclines inhibit the excessive collagen cross linking which results from excessive glycosylation of collagen in diabetes.
Tetracyclines are known to inhibit excessive phospholipase A2 activity involved in inflammatory conditions such as psoriasis as disclosed in U.S. Pat. No. 5,532,227. In addition, tetracyclines are also known to inhibit cycloxygenase-2 (COX-2), tumor necrosis factor (TNF), nitric oxide and IL-1 (interleukin-1).
These properties cause the tetracyclines to be useful in treating a number of diseases. For example, there have been a number of suggestions that tetracyclines, including non-antimicrobial tetracyclines, are effective in treating arthritis. See, for example, Greenwald, et al. “Tetracyclines Suppress Metalloproteinase Activity in Adjuvant Arthritis and, in Combination with Flurbioprofen, Ameliorate Bone Damage,” Journal of Rheumatology 19:927–938 (1992); Greenwald et al., “Treatment of Destructive Arthritic Disorders with MMP Inhibitors; Potential Role of Tetracyclines in Inhibition of Matrix Metalloproteinases: Therapeutic Potential,” Annals of the New York Academy of Sciences 732:181–198 (1994); Kloppenburg, et al. “Minocycline in Active Rheumatoid Arthritis,” Arthritis Rheum 37:629–636 (1994); Ryan et al., “Potential of Tetracycline to Modify Cartilage Breakdown in Osteoarthritis,” Current Opinion in Rheumatology 8:238–247 (1996); O'Dell et al, “Treatment of Early Rheumatoid Arthritis with Minocycline or Placebo,” Arthritis Rheum 40:842–848 (1997).
Tetracyclines have also been suggested for use in treating skin diseases. For example, White et al., Lancet, April 29, p. 966 (1989) report that the tetracycline minocyline is effective in treating dystrophic epidermolysis bullosa, which is a life-threatening skin condition believed to be related to excess collagenase.
Furthermore, studies have also suggested that tetracyclines and inhibitors of metalloproteinases inhibit tumor progression, DeClerck et al., Annals N.Y. Acad. Sci., 732:222–232 (1994), bone resorption, Rifkin et al., Annals N.Y. Acad. Sci., 732:165–180 (1994), angiogenesis, Maragoudakis et al., Br. J. Pharmacol., 111:894–902 (1994), and may have anti-inflammatory properties, Ramamurthy et al., Annals N.Y. Acad. Sci., 732, 427–430 (1994).
Based on the foregoing, tetracyclines have been found to be effective in treating numerous diseases and conditions. Therefore, there is a need for new and even more useful derivatives.